Allergic diseases are among the major causes of illness and disability for all ages in the United States. Food allergy affects about 6% to 8% of children under the age of four, and more than 3.7% of adults in the U.S. More than 23 million people in the United States have asthma. It accounts for ~500,000 hospitalizations each year, was responsible for 3,384 deaths in 2005 and has an annual economic cost of ~$20b. Intense research over the past 30 years has increased our understanding of the pathogenesis of asthma and other allergic diseases. These diseases are caused by an overzealous Th2 immune response to allergens in which immunoglobulin E (IgE) and mast cells play critical roles. Thus, aggregation of high affinity IgE receptor (Fc5RI) by allergen on mast cells results in rapid histamine release and the generation of lipids and cytokines, which are responsible for the manifestations of allergic diseases. The focus of our research has been to study G protein coupled receptor (GPCR) signaling in mast cells. It is generally accepted that agonist-induced GPCR phosphorylation by one or more of the G protein coupled receptor kinases (GRKs) is responsible for receptor desensitization. Unexpectedly, we found that silencing GRK2 expression in human mast cells substantially inhibits Fc5RI-mediated degranulation. Based on this finding, we hypothesize that GRK2 plays a novel role in allergic diseases by promoting Fc5RI signaling in mast cells. In aim #1, we will generate murine bone marrow-derived mast cells (BMMC) with silencing or overexpression of GRK2 in vitro. In aim #2, we will use mast cell knock-in approach to generate mice with mast cell-specific silencing/overexpression of GRK2. Passive systemic anaphylaxis (PSA), bronchoconstriction in precision cut murine lung slices and murine model of allergic asthma will be used to test the hypothesis that mast cell-specific expression of GRK2 is required for allergic responses in vivo. If the outcome of the proposed studies are realized it may provide novel approaches for the treatment of allergic diseases such as food allergy, anaphylaxis, rhinitis and asthma.